Structural health monitoring (SHM) systems are widely used for monitoring structural safety, integrity and performance of a variety of structures such as buildings and aircraft components, among others. Typically, damages such as cracks or delaminations can arise in the material of structures due to high loads or through too high production tolerances. Such damages can considerably weaken the mechanical stiffness and the strength of the components and the overall structure. Especially in connection with an aircraft, the components of the aircraft are also subjected to the danger of impact damages through birds and ice particles during operation. In order to ensure the integrity of such structures, it is desirable to simultaneously monitor the strain, temperature and vibration frequency applied to them in real time.
Strain gauges are used to monitor strain for structures such as aircraft components. Typically, strain gauges are built into mechanical structures to allow continuous or periodic monitoring of defects in the structures. Alternatively, they are retrofitted to structures by being adhered thereto for testing purposes. Such strain gauges provide instantaneous data that is used for real-time monitoring of the structural health of the structures and provide an early warning of a possible unsafe condition.
Unfortunately, the conventional strain gauges used for measuring strain of such structures are usually formed of metals that are quite heavy and are corrosive in nature leading to reliability issues. Moreover, the chemical resistance of such gauges is substantially low along with a substantially low gauge factor resulting in inaccurate and unreliable strain data. In addition, the available strain gauges are anisotropic strain sensors that measure strain in only one direction.